The present invention relates to a method for producing a granular multi-cellular glass (foam glass) and such granular multi-cellular glass produced by the method. More specifically, the present invention relates to a method for producing such glass having high moisture content ratio or water absorption ratio and to a granular multi-cellular glass produced thereby. The present invention also relates to a method for controlling physical properties of the glass and to a granular multi-cellular glass obtained by the control of physical properties thereof.
Granular multi-cellular glass or porous glass grain is light in weight and provides heat insulative characterisitics. Further, the glass generally provides low moisture content ratio or low water absorbing property, and is non-combustible with high moldability. Therefore, the granular multi-cellular glass has been widely available for building materials.
Such granular multi-cellular glass is produced by, for example, injecting gas into molten glass, or by adding and mixing foaming agent with the molten glass and rapidly cooling the mixture by dropping the mixture into cooling medium as described in Japanese Patent Publication No. 51-18968. Alternatively, such glass is produced by the steps of pulverizing glass, adding foaming agent such as carbonate, nitrate and carbon into the pulverized glass, granulating or pelletizing the mixture to a predetermined size, and heating the granulations at a temperature of about from 800.degree. to 1100.degree. C.
Cell size in the granular cellular glass is controllable by controlling distribution of sizes of pulverized glass particles and kind and amount of the foaming agents. Further, final grain diameter of the granular glass is also controllable by controlling cooling temperature for the molten foaming glass, granullation or pelletization degree, and heating temperature, etc.
In this case, the heating temperature is higher than the softening temperature of the glass (about from 710.degree. to 730.degree. C. at which the glass has Poise viscosity of 5.times.10.sup.7). Therefore, the glass hardly provides water permeability, and almost all blisters or seeds in the glass are independent cells (closed cells). As a result, resultant granular multi-cellular glass provides water absorption or moisture content ratio of only from 5 to 20% (vol %) after the glass is at a reduced pressure atmosphere and is subjected to water absorption. In this connection, the glass is usable and applicable to a heat insulating member.
Here, the other types of utility and applicability would be conceivable in the granular multi-cellular glass if moisture content ratio thereof is increased or controlled, and if other physical properties of the glass is controllable. In this connection, various invesitigations have been conducted to increase moisture content ratio of the glass. Through researches and experiments, moisture content ratio has been increased to about 20 to 50% by adding excessive amount of foaming agent to the glass powders, or by adding 5 to 20% of silica sand or diatomaceous earth.
However, thus obtained product is not uniform in its gravity and moisture content ratio and provides low compression strength and low chemical stability.
Throughout the specification and claims, various physical properties are described. The followings are the definitions of these properties:
[moisture content or water absorption ratio] (%): X/Y in which,
X: water volume absorbed in the granular multi-cellular glass (porous glass grain) which is dipped in water at vacuum pressure (about 76 mm Hg) for about 10 minutes, and then at normal atmospheric pressure. PA1 Y: volume of porous glass grain which volume includes volume of pores in which no water is absorbed therein within 1 minute dipping in water at atmospheric pressure. PA1 X: volume of mercury filled in the pores of the porous glass grain at pressure starting from vacuum pressure and ending on 30,000 PSIa by mercury injecting method. PA1 Y: volume of porous glass grain which volume includes volume of pores in which no mercury is filled even at the pressure of 30,000 PSIa. PA1 X: total weight of porous glass grains accumulated in a cylindrical member, PA1 Y: internal volume of the cylindrical member PA1 X: weight of a porous glass grain in air, PA1 Y: volume of the porous glass grain which volume includes the volume of all pores;
[porosity] X/Y in which,
[bulk specific gravity] X/Y in which
[apparent specific gravity] X/Y in which
[absolute specific gravity]
This specific gravity excluding pore portions in the porous glass grain. The absolute specific gravity is equal to (apparent specific gravity)/(1-porosity)
[median pore diameter] (.mu.m)
Each of the pores provides its pore internal volume. The total pore volumes are integrated, and the integrated volume is divided by two. A specific pore diameter corresponding to the half integrated volume is sought. This specific pore diameter is referred to as median pore diameter. In the specification, mercury pressure is increased from vacuum pressure to 30,000 PSIa in mercury injecting method. Increased mercury volumes (intrusion volume into pores) are plotted, with respect to each of the diameters of the pores. Then total volume is divided into two having equal volume to each other. The pore diameter at which the two equal volumes can be defined is referred to as the median pore diameter.
[specific gravity in water]
Specific gravity of the porous glass grain in which water absorbing portions is excluded. That is, weight of the glass grain is divided by apparent volume which volume excludes water volume contained in the glass. The specific gravity in water is equal to (apparent specific gravity)/(1-moisture content ratio),
[apparent specific gravity in water]
Apparent specific gravity of the porous glass grains which contain water therein. The apparent specific gravity in water is equal to (apparent specific gravity) plus (moisture content ratio)
[pore volume (Hg intrusion volume)] (ml/g)
Volume of pores in the porous glass grain having 1 gram in weight. In the present invention, the volume is represented by mercury injecting amount into the pores when the mercury pressure increases from its vacuum pressure to 30,000 PSIa by mercury injection method.